1. Field of the Invention
This invention relates to a multielement acoustic transducer and a method of manufacturing the same. It relates also to an acoustic imaging instrument, particularly an instrument utilizing ultrasonic energy of high frequency.
2. Description of the Prior Art
Heretofore, a scanning acoustic microscope (abbreviated to "SAM") has been proposed by utilizing an ultrahigh-frequency acoustic wave whose acoustic frequency is 1 GHz and whose wavelength in the water is accordingly as short as approximately 1 micron.
More specifically, as shown in FIG. 1, between a transducer 10 for generating a focussed acoustic beam 14 and a detecting transducer 12, a specimen 16 and a speciman supporter 18 which are situated in the focal zone of the acoustic beam are mechanically scanned in the directions of the X- and Y-axes as indicated in the figure. Then, the focussed beam spot scans the speciman surface in the two dimensions. Therefore, when acoustic waves transmitted through and reflected from the specimen are detected by the use of X and Y signals synchronous with the scanning and are displayed on a cathode-ray tube 30 as the so-called Z signal, the two-dimensional acoustic image of the specimen is obtained.
In order to realize the mechanical scanning, it is the practice to employ a moving coil 20 and a coil driver 24 for the fast scanned axis (X-directional scan) and a stepping motor or hydraulic piston 22 for the slow scanned axis (Y-directional scan). Technical problems in such mechanical scanning system are the scanning speed and the scanning area. The former concerns the imaging time of the two-dimensional image (in other words, the period of time required for finishing the image), while the latter concerns the field of view.
On account of the mechanical scanning, there are the contradictory circumstances that when it is intended to take a wide view, the imaging time becomes long and that when it is intended to shorten the imaging time, only a narrow view can be taken. It has heretofore been impossible to realize an imaging instrument of high-speed imaging and wide view. The reasons therefor are that, in general, a mechanical system has the scanning area narrowed more as the scanning speed is higher, and that in order to acquire a detection signal of satisfactory signal-to-noise ratio, a beam spot needs to effectively stay on a scanned point for at least a fixed time.